1. Field
This invention generally relates to wireless communications. More particularly, the invention relates to handoff between a session initiation protocol (SIP) network and a cellular communication system.
2. Background
Table 1 summarizes acronyms and abbreviations.
TABLE 1Acronyms and abbreviationsAPAccess PointAKEYAuthentication KeyBSBase StationCDMACode Division Multiple AccessCFSCNMCandidate Frequency Search Control MessageCFSRSMCandidate Frequency Search Response MessageCFSRQMCandidate Frequency Search Request MessageESNElectronic Serial NumberEVRCEnhanced Variable Rate CodecFAForeign AgentFFSFor Further StudyGPSGlobal Positioning SystemGWGatewayHLRHome Location RegisterHWHardwareIETFInternet Engineering Task ForceIMSIInternational Mobile Subscriber IdentityIOSInter Operability Specifications or ServerIPInternet ProtocolLANLocal Area NetworkMACMedium Access ControlMADMobile Addressed messageMGWMedia GatewayMIBManagement Information BaseMINMobile Identification NumberMIPMobile Internet ProtocolMOMobile OriginatedMSMobile StationMSCMobile Switching CenterMTMobile TerminatedNGLANNext Generation LANQAMOperation Administration ManagementOAM&POperation Administration Management & ProvisioningOCSObiwan Cellular ServerPPPPoint to Point ProtocolQoSQuality of ServiceRFCRequest For CommentsRLPRadio Link ProtocolSGWSignaling GatewaySIPSession Initiation ProtocolSNMPSimple Network Management ProtocolSSSupplementary ServiceSS7Signaling System #7SWSoftwareTCHTraffic ChannelTCPTransport Control ProtocolUDPUser Datagram ProtocolVoIPVoice Over IPVOPSVoice Optimized Power SaveWANWide Area NetworkWSSWireless Soft Switch
SIP-only devices do not have a cellular identity and cannot be granted cellular access without a cellular identity. Thus, there is a need for internetworking SIP-only devices with a cellular network.
One solution has been to statically allocate a cellular identity to every SIP-only device that is planned to have access to a cellular network. This is none standard solution requires changes to the standard SIP protocol in the SIP devices.
In another solution, when a SIP device calls a cellular device, the call can be routed through the public telephony network (PSTN) and in the PSTN the call is routed to a cellular network. This solution introduces extra signaling and traffic overhead which affects the voice quality of the calls. It also introduces extra charges since the call is routed through the PSTN and PSTN operators charge for the call.
Thus, there is a need for a solution that does not require changes to the standard SIP protocol and that does not involve extra signaling and traffic overhead.